France's Free French administration, under pressure from Lebanese nationalists and wartime Allied politics, recognized Lebanese independence after arresting and then releasing Lebanese officials who had unilaterally amended the constitution to remove references to the French mandate. The crisis galvanized public demonstrations and international pressure, forcing France to release the detained leaders and accept Lebanese sovereignty, formally marked on November 22.
The immediate spark had come days earlier when the Lebanese parliament, led by President Bechara El Khoury and Prime Minister Riad al-Solh, voted to amend the constitution and strip out clauses affirming French mandatory authority. French authorities responded by arresting the president, prime minister, and other officials, provoking mass protests and a general strike that spread through Beirut and beyond.
British pressure proved decisive; with the Allies fighting a war partly framed around self-determination, London leaned on the Free French administration of Charles de Gaulle to back down, and the detained leaders were released on November 22, 1943, effectively conceding independence. Full French withdrawal of troops didn't come until 1946, but the political battle had been won.
The day became Lebanon's Independence Day, celebrated with military parades in Beirut, though the young nation's subsequent history — sectarian power-sharing arrangements, civil war, foreign interventions — would test the durability of that hard-won sovereignty again and again.